Polyester, nylon, or rayon yarn is usually produced by polymerization of the synthetic material, free of all water, into small cubes followed by the production of monofilaments from the cubes accomplished by subjecting the synthetic material to melting, and then extrusion thru a large number of small nozzles. The extruded fibers are collected in large cans in the form of what is called "ends". These cans are then arranged at the front end of a stretch line and as many as 40 ends may be combined to form, without twisting, a bundle of monofilaments known as polyester, rayon, or nylon tow. Conventionally, the tow is fed through the stretch line where it is lengthened by stretching, reducing the monofilament diameter and orienting the fiber molecules. The tow may be heat-set on the stretch line, and then crimped and fed to a dryer where it is dried. Alternatively, the tow may be subjected to heat-set as well as drying in the dryer by heating it to a temperature as high as about 250.degree.-400.degree. F. In either case, the crimped tow following drying is cut into short lengths to form staple which is then twisted or spun by a user to produce yarn.
Drying is necessitated by a number of wet treatments during the processing, for instance desulfurizing, washing, and bleaching, following extrusion (U.S. Pat. No. 2,657,433), or other steps depending upon the particular synthetic material employed. Immediately before the drying stage, the tow is a compact but mangled mass which is difficult to dry uniformly because of a small ratio of surface area to unit volume and difficulty of heat penetration into the central filaments. Accordingly, it has been found advantageous and most efficient to dry the tow in a folded condition or a series of laps or plaits, with the lap overlying an adjacent lap. The amount of overlap of successive plaits may be as high as 50-90%.
It is not feasible simply to lay the tow onto a dryer continuous conveyor in successive overlying laps as a leading lap will be positioned beneath the next following lap. At the exit or discharge end of the layer, the tow will then have to be removed by pulling it from underneath more rearward laps and against the conveyor belt, and depending upon the degree of overlap, severe stretch or stretching of the tow and entangling of the tow laps can occur.
It is known to employ a device referred to as a J-box or similar apparatus for the inversion of the tow laps prior to positioning the same on a dryer conveyor. An example of such an apparatus is shown in British Pat. No. 1,121,486, for instance in FIG. 8 of the patent. Generally, the J-box is in the form of an open top chute, having a rectangular cross section and in an elevation sideview, a J configuration with a generally vertical upper long leg and a shorter lower leg sloping downwardly at an angle to the vertical leg. Lengths of fabric are folded into the J-box upper open end, and the weight of the piled-up material forces the same to pass downwardly in the J-box exiting through the short leg onto a conveyor. By virtue of the general shape of the J-box, the folds (laps or plaits) come to rest on the conveyor in an approximate upright position.
In the apparatus of the '486 patent, means are provided to lay the tow material in the top of the J-box in horizontal, short folds which extend back and forth from front to back, viewed from the side of the apparatus. The short folds have a lot of resilience and spring action and, hence, move uniformly down the J-box onto a conveyor.
The present invention by contrast is concerned with plaiting tow in relatively long laps or plaits which extend from side to side, for instance three to six foot laps. Whereas the short webbing folds have resilience and spring action, tow when plaited from side to side in long laps does not have such resilience or spring action. Further, the tow at one point may have a very rectangular cross-section, so that it extends fully between the front and back sides of the J-box, and at another point a more square cross-section so that it is spaced from the sides. As the tow laps travel downwardly in a J-box, confined by the parallel sides of the box, tow which is relatively thin in cross-section will meet less resistance and tend to compress more than tow of thicker cross-section. If this variable compression is translated to the tow deposited on the conveyor, the frequency of laps on the conveyor will vary, resulting in non-uniform drying of the tow. The situation can be aggravated further if tow of unusually high thickness enters the J-box and becomes held up by the sides to the extent that stoppage of the flow of tow results.
A variation of the J-box structure is also illustrated in the '486 patent, for instance in FIG. 6. In this environment, a pair of rollers move to and fro serving as a folding device for laying tow material onto the upper side of a revolving perforated drum, the rollers moving horizontally and at right angles to the axis of the drum. The drum has the purpose of inverting or what is called reversing the folds of material and passing them to a subsequent conveying means. This is accomplished by employing a curved vibrator conveyor spaced a certain distance from the drum and adapted to the curvature of the drum. Material folded onto the drum is guided on both sides by the drum and vibrator conveyor for a certain distance until substantially diametrically opposite the folding point. At this opposite point, the folds of material leave the surface of the drum in an orientation such that they can be drawn off at a discharge end without damage. This embodiment or structure, as with the J-box structure, is suitable for short folds of tow which have resilience or spring action, but the apparatus lacks suitability for use with longer laps up to three to six feet in length, which have little resilience and spring action. To plait tow across the entire width of the apparatus onto an upper curved surface can easily result in uneven layer down of the tow and uneven movement of displacement of the laps at one side of the apparatus compared to the other side.
A similar device is shown in a Wetzler U.S. Pat. No. 3,332,595. In this patent, there is shown an endless belt conveyor between two sprockets onto which the tow is deposited, in an undulating back and forth movement similar to that of British Pat. No. 1,121,486. Here also, the short webbing folds have resilience and spring action and will move as shown in the patent. In contrast, tow when plaited side to side does not have such resilience or spring action and hence will not be inverted. In addition, there is provided in the Wetzler patent an outer curved wall spaced from the conveyor belt, which extends below the belt downwardly to a second horizontal conveyor. In the area between the upper conveyor belt and the lower conveyor belt, long tow plaits or laps would be virtually unsupported, and would tend to randomly tumble down to the lower conveyor belt and become nonuniformly positioned on the lower belt.